CHS refinery officials are investigating the cause of a butane release while the gas was being unloaded from a rail car last month.

The release of about 2,100 gallons of butane happened Oct. 21, CHS Manager Pat Kimmet said today. No one was injured and safety gas meters did not detect any hazard, he said. The release occurred about 60 feet from the ground and no one was in the area at the time.

An investigation into the cause and corrective action began immediately and is continuing, Kimmet said.

A safety bulletin from the Laurel oil refinery described the release as "a significant near miss.''

The leak occurred as the refinery was starting up a capital project for new lines to butane tanks. Butane was being transferred from a rail car and hit a block in the line. The refinery stores butane in spherical tanks and uses it in processing. Butane is flammable.

Shortly after the unloading began, a vapor cloud was seen at the tank from an office in the administration building, the bulletin said. The unloading was immediately stopped.

The amount of butane released did not require the refinery to report the incident to regulators, Kimmet said.